When dealing with unusual pieces of vinyl flooring, it helps to take a piece of scrap paper to use as a template. This helps when it comes to cutting the piece and to ensure a proper fit when you go to place it down.
When repairing damage around a hole you want to be extra careful. For a recessed light in drywall, ensure you put fibre mesh tape on both sides of the drywall and fill with compound. This will take multiple coats but when doing so make sure you don't put it on too heavy as it will sag down on you
When making a custom molding that must be curved, ie. around a stairwell, you need to puts slits in it with a hacksaw about every inch or so to allow it to curve. This is used to cover the transition between vinyl flooring and where that meets the spindles.